ADPKD is the most common hereditary kidney disease, affecting 1 in 400 to 1000 individuals and accounting for 4% of end-stage renal disease in the United States and 8-10% in Europe. The condition is characterized by progressive development of kidney cysts with kidney enlargement and associated loss of kidney function. High blood pressure and cardiovascular disease are common in patients with ADPKD. Although the condition is often thought to affect primarily adults, it is clear that the disease can be present in the fetus and young children. This study is designed to determine if treatment with the medicines, pravastatin and lisinopril, can slow the progression of kidney and heart disease when initiated early in life in patients with ADPKD. The goal of this randomized double-blind placebo-controlled trial is to determine whether treatment with the 3-hydroxy-3- methylglutaryl coenzyme A (HMG coA) inhibitor pravastatin will delay the progression of renal and cardiovascular disease over a three-year period in children and young adults with autosomal dominant polycystic kidney disease (ADPKD) who are receiving angiotensin converting enzyme inhibitors. The primary endpoint of the study will be achieved in subjects with 20% or greater change over the three-year interval in any or all of the following four endpoints: 1) total renal volume as assessed by MRI; 2) left ventricular mass index as assessed by MRI; 3) urinary albumin excretion; and 4) endothelial-dependent vasodilation as assessed by brachial ultrasonography. This study will involve pediatric subjects because we believe that early intervention is critical if we are to ameliorate the morbidity and mortality associated with this condition. If pravastatin is shown to be effective in ameliorating progression of renal and cardiovascular disease in this study, routine management of affected patients will be drastically altered.